Is Jatropha a miracle crop producing high yields on marginal lands?

Quote: “Prior to 2007, Jatropha curcas Linn. was promoted as a miracle crop capable of producing biofuel from marginal and degraded lands.”

Plant growth can be understood based on production ecological principles (1). We can distinguish between the production-defining factors radiation, climate and plant genotype; the production-limiting factors nutrients and water; and the production-reducing factors pests, diseases and pollution (figure in enhancement). In the absence of limiting and reducing factors, we speak of the potential production of a specific crop in a specific location. The difference between potential and actual yield is called “yield gap,” and depends on the prevalence of reducing and limiting factors, and the extent to which management can overcome these. Whether management interventions to decrease the yield gap are indeed applied depends on input-output price relations and social factors such as skills of the farmers, access to production factors and output markets, and on the relative importance of crop production to people’s livelihoods.

The phrase “marginal land” has many definitions. One explanation of marginal refers to soils that are of insufficient quality to support crop production, being too dry (deserts), too wet (swamps), too salty, too acid, too compact, containing high levels of aluminum, or having low nutrient availability (either degraded or inherently poor). Another definition of marginal land includes distance to input and output markets and lack of infrastructure, focusing on the remoteness of the land, which makes its cultivation economically unattractive. Some people refer to marginal lands as those lands that have been abandoned after deforestation or crop cultivation, perhaps due to degradation and decreasing yields or to a change in market opportunities and decreases in output prices.

In Indonesia jatropha is promoted as an alternative to oil palm, as it can grow in agro-ecological zones where oil palm cannot produce due to low rainfall. In several places (Maumere, Sikka in East Nusa Tenggara; Biak Island, Irian Jaya; and Gunungkidul, Yogyakarta in Central Java) jatropha plantations were used to restore degraded lands, being planted on hills and rocky soils.

So how to understand the relation between jatropha production, agro-ecological production principles and marginal lands?

As jatropha is a newly domesticated crop, its production potential has not yet been established. There are no stable varieties as a result of breeding yet, and the genotype by environment by management interactions are still poorly understood. What is clear is that the optimistic yield expectations have not yet materialized. Jongschaap et al. already concluded in 2007 that claims of high jatropha oil production resulting from low-nutrient requirements (soil fertility), low water use, low labor inputs, and tolerance to pests and diseases are definitely not true (2). They also stated that all studies that express yields per tree should be carefully analyzed and evaluated to avoid misinterpretation and the neglect of competition effects in plantations and intercropping. Van Eijk et al. assessed jatropha plantings in 2010 and found that there is a lack of systematic investigation of production data, of the effects of pruning, and of jatropha performance in hedges and intercropping (3). Furthermore, no methodologies have as yet been developed to investigate the response of jatropha to radiation, temperature, fertilization and irrigation. There is no comparison between the jatropha genotypes available, and information on genotype performance on marginal land is not known.

Given these findings, we have three ways of dealing with the issue.

A first option is to identify genotype by environment interactions, which still leaves us with the question of what we call a genotype. Dr. Ruly Dyah Purwati of the Indonesian Agency for Agricultural Research and Development (IAARD) used conventional breeding to increase productivity, aiming at traits such as number of capsules/shrub as a proxy for dry-seed yield and oil yield (4). The IAARD performed multi-locational trials with jatropha germplasm collected from different locations and with three Improved Populations (IP): IP1 (>200 capsules/shrub: potential yield of 1 ton/ha), IP2 (>400 capsules/shrub: potential yield of 2 tons/ha) and IP3 (>600 capsules/shrub: potential yield of 3 tons/ha). Depending on the provenance of the germplasm, IPs were made for dry (IP-A), medium dry (IP-M) and wetter areas (IP-P).

In 2008, Balittas announced that they produced and sold jatropha seed suitable for planting in the dry (IP-2A), moderate (IP-2M) and wet (IP-2P) climates. Source: Balittas (Indonesian Sweetener and Fiber Crops Research Institute).

Twelve genotypes were planted in the following four locations: East Java, Central Java, Gunungkidul, North Lombok. Yields for the first year, measured in December 2011, varied between 215 and 857 kg/ha. East Java had the highest average yield (687 kg/ha), followed by North Lombok (504 kg/ha); the other two locations yielded 456-458 kg/ha on average. No single one of the genotypes performed best in all the environments, hence genotype by environment interactions were important. Even in their own environments IP3A, IP3M and IP3P did not do better than several of the other genotypes tested, indicating that breeding programs need to be strengthened with more germplasm.

Mediterranean soils with calcareous stone distributed throughout the first horizon and limestone beneath. Vegetation in the photos shows the different types of plants adapted to the poor soil. Photo: Juliana Tjeuw, Gunungkidul 2011.

A second option is to cultivate jatropha on marginal soils, but provide the inputs (nutrients and water) needed to improve production. To optimize management of seed production, and to assess whether this management is economically rational, many agronomic experiments need to be performed. Firstly, it is important to understand plant physiology and the effects of water and nutrient management on seed production. Complicating factors are plant density, pruning and timing of management interventions, as well as the interference of pests and diseases. The behavior and productivity of jatropha may differ, depending on whether it is cultivated in monoculture, hedges or intercropping, due to above- and belowground interactions between plants.

Jatropha as a hedge to protect maize crops from browsing goats and other livestock. Photo: Juliana Tjeuw, Sumbawa, February 2011.

An experiment was performed on pruning jatropha in hedges (10 or 30 cm planting density) until they were 50 cm aboveground, and in two-year-old monoculture (21 x 2 m) until they were 75 cm aboveground (5). All jatropha were treated for pests and diseases. The average dry-seed yield for jatropha hedges with a planting density of 10 cm was not statistically different between pruned trees and the control trees, 3.1 g/tree and 5.2 g/tree respectively. The average seed yield for jatropha hedges with a planting density of 30 cm was significantly different for pruned trees, 10.8 g/tree in comparison to the control trees at 2.91 g/tree, t(46)=15.271, p<0.001. For the monoculture, the average seed yield for pruned jatropha was significantly reduced to almost half that of the non-pruned jatropha: 5.4 g/tree instead of 10.2 g/tree, t(84)=3.698, p<0.001.

Figure 1 Dry-seed yields (g/tree) of pruned and non-pruned jatropha trees in hedge system with planting density of 10 cm and 30 cm and in two-year-old monoculture system with planting density of 2×2 m. Different letters in each experiment indicate that the values are significantly different at p<0.001; ns=not significant at p<0.05.

In the seed garden of in Balittri (Indonesian Industrial and Beverages crops Research Institute)these six year old jatropha trees were productive because they were pruned and weeded. Photo: Juliana Tjeuw, February 2011

This three year old jatropha in monoculture at a farmer’s site in Sumbawa was not pruned or weeded. Photo: Juliana Tjeuw, 2011.

As expected, pruning was beneficial for seed yield per tree in 30 cm hedges, reducing aboveground competition and increasing the number of new branches, which are the ones bearing fruit. In the 10 cm density hedges, pruning did not improve seed yield, probably because competition was high for the new branches as well. In the monoculture, the pruned trees were affected by fungi, reducing productivity.

A third option is to adapt the jatropha plant to being grown in adverse soil conditions. In Indonesia there are 47.5 million ha of yellow red podzols soils (acid and high aluminum) and 25 million ha of peat soils (acid). Dr. Sony Suharsono from the Research Center for Bioresources & Biotechnology (IPB) in Bogor, Indonesia, works on genetic engineering of jatropha involving the genes for aluminum tolerance. Plants have at least three different mechanisms for dealing with high Al toxicity (6): 1. synthesis of high organic acids such as malate and citrate; 2. synthesis of antioxidants such as superoxide dismutase; and 3. synthesis of binding proteins such as metallothionein. Genes expressing for the synthesis of these substances are interesting candidates for incorporation into jatropha, allowing it to grow on marginal (aluminum toxic) soils. Dr. Sony Suharsono also used genetic engineering to increase productivity through increasing the number of female flowers (only the female flowers lead to seeds), based on the Hd3a gene from rice and the IMA gene from the tomato. This work has been executed in IP2P, IP3A and IP3M, building upon the results of the conventional breeding by IAARD.

Given the lack of scientific progress, we must conclude that jatropha is not (yet) producing high yields on marginal lands. In other species that are currently commercially grown, such as oil palm, selection and breeding took numerous years and is ongoing. Therefore, we cannot exclude the possibility that jatropha varieties which will produce high oil yields will also be developed, especially when conventional breeding and genetic engineering go hand in hand. The production ecological concepts already clarify that a yield gap will occur when plants have to grow in circumstances without adequate soil nutrients and water. In breeding programs, the positive response of the plant to inputs (water, fertilizer) is generally an important breeding goal. It will therefore be highly unlikely that high-yielding varieties will produce high oil yields in marginal lands without additional inputs, even in the future.

Test field with four year old pruned jatropha intercropped with maize. Local casual labourers are weeding maize planted in between rows of jatropha. Photo: Juliana Tjeuw, Gunungkidul 2012.